1. Field of the Invention
This invention relates to a strapping machine, particularly to one installed with a simple automatic band conveying device able to easily and automatically transmitting a band by means of an electromagnetic valve to drive a connecting rod to push a pressing plate to press on a band rail.
2. Description of the Prior Art
As shown in FIGS. 1 and 2, a conventional automatic band conveying device includes a band conveying device 10 used to transmit a band 11 into a band rail 12, and a pressing rail device 20 which is composed of a gear motor 21, a brake 22, a band passage pressing rod 23 and a proximity switch 24. The gear motor 21 is fixed at one side of the band rail 12. The brake 22 and the band passage pressing rod 23 are orderly mounted on a rotating axis 211 of the gear motor 21. By means of the proximity switch 24, the rotating axis 211 of the gear motor 21 can drive the band passage pressing rod 23 to rotate for a preset angle. And, the gear motor 21 is then to be stopped by the brake 22 to keep the band passage pressing rod 23 pressing on a band passage 13 of the band rail 12 for the band 11 to pass through to a lower separate mechanism 14. Next, the brake 22 can automatically release the gear motor 21 to let it rotate in reverse and the band passage 13 is elastically pushed back to its original position by a compression spring 15. However, in operation, the position and the rotating direction of the gear motor 21 and the brake 22 must be detected and controlled by the proximity switch 24, creating a complicated operation to be apt to pose a shutdown or a breakdown of the conventional automatic band conveying device. Moreover, with too many proximity switches 24 used in the conventional automatic band conveying device, not only the operation is much lowered because of frequent malfunction of the proximity switch 24, but also the cost is high.